Police scour Wanda Beach following the murders, 1965. Source: The Daily Telegraph

Marianne Schmidt in undated family photo, who was found murdered along with friend Christine Sharrock at Wanda Beach in Sydney in 1965. Source: The Daily Telegraph

Cold Case: Christine Sharrock and Marianne Schmidt. Source: The Daily Telegraph

Christine Sharrock in undated family photo, who was found murdered along with friend Marianne Schmidt at Wanda Beach in Sydney in 1965. Source: The Daily Telegraph

A NEWLY discovered blood spot may hold vital DNA evidence that could solve one of Sydney's most enduring mysteries.

The blood, taken from the scene of the Wanda Beach murders 47 years ago, belongs to an unknown male and was gleaned from crime scene boxes after cold case detectives revisited the case.

Now police hope new testing methods will give them a fuller profile and provide a breakthrough in the case.

Murders that still haunt our state

Teenagers Marianne Schmidt and Christine Sharrock were found stabbed and bashed to death in the sand dunes at Wanda beach, in Sydney's south, in January 1965. Despite a number of investigations over the years no one has ever been arrested for the murders of the two 15-year-olds from Ryde.

The Cold Case Squad was told to reinvestigate the case by Police Commissioner Andrew Scipione in 2007.

The Cold Case Justice program located clothing belonging to the Wanda Beach victims, had crime scene negatives reprinted and reviewed all the evidence.

A button and zipper were removed from one of the victim's shorts and a sub sample sent to New Zealand for DNA testing but the profile which came back belonged to one of the victims.

Surprised that DNA profiles could still be obtained from a sample so many years old, officers decided to test a blood mark on the shorts that could be a knife wipe mark. A weak male profile was found.

Assistant Commissioner Mark Sweeney, head of the forensic group, said: "We are optimistic that when enhanced with new techniques the DNA could be used against a number of known suspects. What it shows is DNA can be successfully extracted nearly 50 years later and science used to investigate new and old crimes."

Police are being cautious and at the moment it is believed the DNA markers are not strong enough for a conclusive comparison. However, testing methods are improving and the sample will undergo further tests as the technology becomes available. Police won't say if they have a suspect in mind to match the DNA against.

However, other sources have revealed a number of suspects are still alive.

"There is one in particular that I would love to see matched against any DNA we may get in the future," the investigator said. "Luckily he is incarcerated interstate and will never be released." Last year the Cold Case squad cleared more than 33 sex assaults and several murders committed as far back as the early 1980s.

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DNA clue to Wanda Beach murders